A variety of modalities, ranging from cartilage transplant to pharmaceuticals, have demonstrated considerable promise as methods for altering the progression of osteoarthritis. This has resulted in heightened interest in methods for assessing early osteoarthritic cartilage changes both in humans and animals. The objective of this proposal is to improve current animal models for the evaluation of therapeutics designed to treat osteoarthritic cartilage. Specifically, the hypothesis of this work is that Optical Coherence Tomography (OCT), when combine with rabbit and rat models of osteoarthritis, will demonstrate unique advantages for the evaluation of potential therapeutics. This program is a continuation of an ongoing collaboration between investigators at Brigham and Women's Hospital and King's College. It is postulated that the proposed model, in addition to increasing information on the efficacy of therapeutics, will reduce the number of animals that need to be sacrificed, the quantity of tissue requiring processing, and the amount of therapeutics required. Furthermore, technological advances can be directly transferred to in vivo human applications. The hypothesis of this proposal will be tested both through technology development and animal studies. The specifics aims are: Aim 1. To construct a constant velocity polarization rotator for the OCT system. Aim 2. To development an OCT arthroscope capable of accessing a joint through a 20 gauge needle. Aim. 3. To validate registration of the arthroscopic based system. Aim 4. The OCT system will be tested in a rabbit model. Aim 5. A catheter will be developed to image in a rat model. Aim 6. The OCT imaging catheter will be tested in a rat model.